Tokkai Hei 4-297330 published by the Japanese Patent Office in 1992 and Tokkai Hei 8-251708 published by the Japanese Patent Office in 1996 disclose a so-called parallel hybrid vehicle drive system wherein the output torque of an engine and a motor/generator are input to drive wheels via a continuously variable transmission.
In this device, the motor/generator operates as a motor when power is supplied from a battery, and applies a rotation torque to the drive wheels. On the other hand, when a rotation torque is input from the drive wheels, so-called regenerative braking is performed wherein the motor/generator generates power and charges the battery. The drive ratio of the continuously variable transmission, that is the input speed/output speed, varies according to the vehicle speed and throttle opening of the engine.
When the vehicle speed falls due to operation of the brake, the drive ratio of the continuously variable transmission tends towards a maximum drive ratio, and an engine braking force or motor/generator regenerative braking force depending on the increasing drive ratio acts on the drive wheels together with the braking force of the brake.
In such a vehicle, when an antilock braking system (ABS) is applied to prevent locking of the drive wheels during braking, an engine braking force or regenerative braking force is acting even when the braking force is limited by the antilock control, so the braking force tends to become excessive.